Laboratoire de Physique Theorique d'Orsay
 Bâtiment 210 Univ. Paris-Sud 11 91405 Orsay Cedex France T. 01 69 15 63 53 F. 01 69 15 82 87

 Agenda > Séminaires / Seminars > Particules Dernier ajout : jeudi 2 octobre 2014.

# Séminaires Particules 2010-2011

 Les séminaires se tiennent en salle 114 au 1er étage du bâtiment 210, généralement le jeudi à 16h, sauf indication contraire. Contact pour les séminaires : Benoît Blossier.   Jeudi 7 Juillet 2011 à 16h, salle 114 Jean-François Mathiot (LPC Clermont-Ferrand) : Etats liés relativistes sur le front de lumière La dynamique relativiste sur le front de lumière est l’une des trois formes de dynamique proposées en 1949 par P.A.M. Dirac. La description des processus physiques à très haute énergie sur le front de lumière, en diffusion profondément inélastique par exemple, est maintenant bien connue. La description relativiste de la structure d’états liés en dynamique sur le front de lumière peut paraître plus surprenant. Nous passerons en revue les intérêts de cette description, et les développements récents liés d’une part au contrôle stricte de l’invariance par rotation, et d’autre part à la mise au point d’un schéma de renormalisation nonperturbatif approprié. Nous présenterons quelques résultats significatifs dans le modèle de Yukawa.   Jeudi 28 Avril 2011 à 16h, salle 114 François Arleo (LAPTH Annecy) : Phenomenology of prompt photon production in p A and A A collisions The production of prompt photons in proton-nucleus collisions is a promising tool to probe nuclear parton densities, which are presently poorly constrained. Using the most recent nPDF sets currently available, NLO predictions at RHIC and LHC will be presented. I will then discuss the double inclusive production of a prompt photon in association with a heavy-quark jet in Pb-Pb collisions at LHC. This process is shown to be sensitive to the energy loss of heavy-quarks in quark-gluon plasma.   Jeudi 14 Avril 2011 à 16h, salle 114 Vittorio Lubicz (Université de Rome) : Isospin Breaking Effects from Lattice QCD We present a new method to precisely evaluate with lattice QCD the leading isospin breaking effects due to the small mass difference (md-mu) between the up and down quarks. The method is applicable in principle to any hadronic observable which can be computed on the lattice. In this talk, we illustrate the physical interest of this study, describe the method and present preliminary results for several quantities of interest. These include a determination of the quark mass difference (md-mu) itself and of the isospin breaking effects in the kaon decay constant and the form factors of semileptonic $K\ell 3$ decays.   Jeudi 7 Avril 2011 à 16h, salle 114 Jose Miguel No (CEA IPhT) : Cosmological 1st Order Phase Transitions : Electroweak Baryogenesis and Gravitational Wave Production A cosmological first order phase transition can lead to many interesting phenomena, such as electroweak baryogenesis or the production of a stochastic background of gravitational waves. The phase transition procees through the nucleation and subsequent expansion of bubbles, and the understanding of the dynamics of their expansion is very relevant for the study of these phenomena. In particular some quantities, like the bubble wall velocity or the energy efficiency coefficients (for converting the available free energy of the Higgs field into fluid bulk motion, thermal energy and gradient/kinetic energy of the Higgs field) play a key role. I will first review the hydrodynamic treatment used to describe the fluid motion once bubbles start growing, and obtain the energy conversion efficiency coefficients that allow the energy budget of the phase transition to be analyzed. Then I will comment on some recent developments on the process of bubble expansion in cosmological phase transitions, like the existence of continuosly accelerating ( ?runaway ?) bubbles or the possible occurence of hydrodynamic obstructions, and explain how they modify the previous analysis.   Mardi 5 Avril 2011 à 16h, salle 114 Jorge C. Romão (Instituto Superior Técnico, Lisbon) : Lepton Flavour Violation and Dark Matter in SUSY Seesaw Model We review Lepton Flavour Violation (LFV) and Dark Matter (DM) in the supersymmetric version of the seesaw mechanism (type I, II and III) and in Left-Right (LR) models. The LFV needed for explaining the neutrino masses and mixings acts as the only source of LFV and has experimental implications both in low-energy experiments (like MEG) where we search for the radiative decays of leptons, and at the LHC where we look at its imprint on the LFV decays of the sleptons and on slepton mass splittings. We discuss how the confrontation of slepton mass splittings as observed at the LHC and low-energy LFV observables may provide important information about the underlying mechanism of LFV.   Jeudi 31 Mars 2011 à 16h, salle 114 Diego Guadagnoli (LPT) : On the consistency between CP violation in the K vs. Bd-meson systems within the Standard Model In the K and Bd systems, indirect CP violation is quantified by the parameters epsilon_K and sin 2 beta, respectively. Within the Standard Model, the uniqueness of the CP violating phase implies that the measurement of either between epsilon_K and sin 2 beta permits to predict the other. Since both these parameters are very well measured, this turns into a powerful test of consistency. I discuss the status of this test, especially in the light of recent advances on the epsilon_K formula. I will argue that, at the moment, this test is less than perfect.   Mardi 29 Mars 2011 à 16h, salle 114 Konstantin Petrov (CEA IRFU/SPhN) : Finite Temperature QCD from the lattice I will review recent developments in QCD at finite temperature using lattice simulation technique. In particular, such fundamental questions as the transition to quark-gluon plasma and quarkonium dissolution will be in focus of the presentation. Across the phase boundaries and Atlantic ocean - how close are we in our quest for continuum ?   Vendredi 25 Mars 2011 à 11h, salle 114 Cyrille Marquet (CERN) : Probing the nuclear structure at small-x with high-energy e+A collisions Our present knowledge of the nuclear structure at small-x is not sufficient to quantitatively understand relativistic heavy-ion collisions. I explain how different processes in e+A deep inelastic scattering allow to extract important information about the distribution of small-x gluons in nuclei. In particular I will discuss the impact-parameter and transverse momentum dependence of the gluon distribution, as well as multi-gluon correlations which are equally important at small-x.   Jeudi 24 Mars 2011 à 16h, salle 114 Franco Buccella (Université de Naples et INFN) : Leptogenesis with Right-handed Neutrinos Compact Spectrum The demand of a compact spectrum for right-handed neutrinos at the scale of B - L spontaneous symmetry breaking in SO(10) unified theory with Pati Salam intermediate symmetry flavours the realization of the leptogenesis scenario and gives predictions for the parameters of the left-handed mass matrix not fixed by oscillation experiments. As a consequence one predicts for the cosmological relevant sum of neutrino masses a value slightly higher than the present lower value, which is not very far from the present upper value. For the mass parameters relevant in tritium and neutrino-less double beta-decay the predicted values are more than two orders of magnitude smaller than the present upper limits.   Mardi 22 Mars 2011 à 16h, salle 114 Carlos Yaguna (Université de Madrid) : Three-body final states in dark matter annihilations and decays In dark matter studies, the annihilation rate of dark matter particles plays a crucial role, for it determines their relic density and their indirect detection signal. I will show that this annihilation (or decay) rate can receive large additional contributions from three-body final states consisting of a real and a virtual massive particle, such as WW* (Wff’) and tt* (tWb). As a result of these previously neglected processes, the viable parameter space of dark matter models is modified and the predictions for the direct and the indirect detection of dark matter are significantly altered. I will illustrate the relevance of these effects in supersymmetric and non-supersymetric scenarios.   Mardi 15 Mars 2011 à 16h, salle 114 Aberto Ramos (CPT Marseille) : Nucleon sigma terms and electromagnetic correction to light hadrons from the lattice Thanks to the recent developments both in our understanding of lattice simulations and in computer power, lattice gauge theory can give results of QCD with all the sources of error under control. During the talk I would try to convince you that lattice QCD is of key importance first to understand direct detection of dark matter : I will present you some results on the octet baryon sigma terms. Also I will detail our program of describing the standard model at low energies, thus requiring the introduction of QED in our simulations.   Jeudi 10 Mars 2011 à 16h, salle 114 Carlotta Pittori (ASI Science Data Center) : AGILE and Fermi satellites : recent highlights in gamma-ray astrophysics In this talk I give an overview of the latest highlights in high-energy astrophysics from AGILE and Fermi missions, currently operating together in space. Gamma-ray emission from cosmic sources at energies above 100 MeV is intrinsically non-thermal, and the study of the wide variety of observed Galactic and Extragalactic gamma-ray sources provides a unique opportunity to test theories of particle acceleration and radiation processes in extreme conditions, and it may help to shed light on the foundations of physics itself.   Jeudi 3 Mars 2011 à 16h, salle 114 Roland Kirschner (Université de Leipzig) : End point contributions in exclusive production Singularities at the end point values of the parton momentum fractions may appear in intermediate steps of calculations of hard exclusive processes. We discuss contributions of bremsstrahlung and of higher twist removing these singularities. The approach of avoiding the singularities by including a Sudakov formfactor is criticized. The singularities are artefacts of an incomplete treatment of the collinear limit.   Mardi 22 Février 2011 à 16h, salle 114 Roberto Franceschini (EPF Lausanne) : The effective W approximation for WW scattering and new physics In this talk I review the motivations and the prospects of the study of the scattering of W boson. The details of the mechanism of electroweak symmetry breaking that can be unveiled will be presented. The issue of the extraction of WW -> WW scattering amplitudes from the study of physical processes initiated by fermions, i.e. qq -> qqWW, will be addressed using the effective W approximation. A discussion of the regimes of validity and of the expected corrections to the effective W approximation will be presented.   Mardi 15 Février 2011 à 16h, salle 114 Svjetlana Fajfer (Physics Dept. University of Ljubljana and J. Stefan Institute, Ljubljana) : Light colored scalars and the up quarks phenomenology A colored weak singlet scalar can accommodate the 2 sigma disagreement of the measured forward-backward asymmetry from the Standard model prediction in the t - bar t production at the Tevatron. Such colored scalars appear in a class of grand unified theories. Their couplings to up quarks can be fully constrained using D - bar D oscillation observables, as well as di-jet and single top production measurements at the Tevatron. After making predictions for the flavour changing neutral current transitions in the charm and top quark sectors, we discuss the impact of these constraints on the texture of the up-quark mass matrix within a class of grand unified models.   Jeudi 10 Février 2011 à 16h, salle 114 Christopher Smith (IPN Lyon) : Minimal Flavor Violation In the past few years, the Minimal Flavor Violation (MFV) hypothesis has emerged as an appealing framework, allowing to reconcile the ever more constraining low-energy data with the possibility of New Physics below the TeV scale. In this talk, after a brief introduction, several aspects of its implementation are reviewed in the context of supersymmetric theories. First, CP violation in the MFV framework is revisited, showing that new phases are unavoidable. Second, if MFV is assumed to hold already at the GUT scale, its evolution exhibits IR fixed-points, translating as definite predictions for flavor-violating observables. Finally, enforcing MFV on baryon and lepton number violating interactions is shown to be sufficient to prevent a too fast proton decay. MFV is thus a viable alternative to R-parity, opening the door to additional channels for discovering supersymmetry at colliders.   Mercredi 9 Février à 11h, salle 114 Andrey Tayduganov : Determining the photon polarization of the b —> s gamma using the B —> K_1(1270) gamma —> (K pi pi) gamma decay Recently the radiative $B$ decay to the strange axial-vector mesons, $B\to K_1(1270) \gamma$, has been observed with a rather large branching ratio. This process is particularly interesting as the subsequent $K_1$ decay into its three body final state allows us to determine the polarization of the photon, which is mostly left (right-)handed for $\overlineB (B)$ in the SM while various new physics models predict additional right- (left-)handed components. A new method is proposed to determine the polarization, exploiting the full Dalitz plot distribution, which seems to reduce significantly the statistical errors. This polarization measurement requires however a detailed knowledge of the $K_1 \to K \pi \pi$ strong interaction decays, namely, the various partial wave amplitudes into the several possible quasi two-body channels, as well as their relative phases. The pattern of partial waves is especially complex for the $K_1(1270)$. We attempt to obtain the information through the combination of an experimental input and a theoretical one, provided by the $^3P_0$ quark-pair-creation model.   Vendredi 4 Février 2011 à 14h, salle 114 (séminaire commun LPT/IPN) Yuming Wang (Université de Siegen) : Applications of k_T factorization approach in exclusive processes I will briefly review the basis idea of k_T factorization approach, and then show that k_T factorization provides a systematical way to investigate the exclusive processes without introducing any infrared regulator in the leading power of 1/Q (1/m_Q). NLO correction to pion form factor will be illustrated to explain how the collinear divergences in the quark diagrams are absorbed into the pion wavefunctions and the soft divergences cancel among themselves. Applications of k_T factorization in hadronic B decays will be also discussed in detail. Comparisons of k_T factorization approach with QCDF, SCET and LCSR will be presented both conceptually and phenomenologically.   Jeudi 3 Février à 16h, salle 114 Julien Baglio (LPT) : Higgs boson(s) at hadronic colliders : from the Standard Model to SUSY The Higgs boson, the key component of the electroweak symmetry breaking of the Standard Model and at the origin of mass, is still evading direct experimental evidence. We will discuss in this seminar its production and decay modes at the two main hadronic colliders in current activity, the Fermilab Tevatron collider and the CERN Large Hadron Collider, both in the Standard Model and its minimal supersymmetric extension. We will analyse the theoretical uncertainties affecting the predictions and show that they can have a drastic impact on the theoretical inferred limits.   Lundi 31 Janvier 2011 à 11h, salle A201 du Batiment l’IPN (séminaire commun CPhT/IPN/LPT) Ziguo He (Université de Barcelone) : Charmonium Production at B-factories In this talk, I will review the recent theoretical progresses in charmonium electro-production within the framework of non-relativistic QCD (NRQCD) factorization approach. In the double charmonia production case, e+e− ! J/ +-c(-c0), we found that the contribution of relativistic corrections is as important as that of the next-to leading order (NLO) QCD corrections. After combining the relativistic corrections with the NLO QCD corrections, the large gap between leading order NRQCD predictions and experimental measurements, is almost removed. In the e+e− ! J/ +c¯c+X case, the NLO QCD corrections also explain the puzzle of J/ production in association with c quark pair at B-factories. In the J/ + Xnon−c¯c production case, after taking into account the relativistic corrections and NLO QCD corrections, the color-singlet contribution itself could explain the J/ +Xnon−c¯c production at B-factories, which leaves very little room for the color-octet contribution in NRQCD. In addition, the charmonium production recoiling against one photon process is found to be helpful to clarify the nature of the newly discovered states X(3940) and X(3872).   Jeudi 27 Janvier 2011 à 16h, salle 114 Siba Prasad Das (Université de Valence) : Rare decays and CP violating Higgs at MSSM and beyond We address the Higgs boson mass constraints from a theoretical perspective focussing on the Minimal Supersymmetric Standard Model(MSSM) that offers the stabilization of the masses of the Higgses from radiative corrections. We discuss the weak rare decays of mesons, flavor violating decays of top quark and Higgs boson in a generic two—Higgs Doublet Model(2HDM), of which the Higgs sector of the MSSM is a variant. In the second part of this talk, we show the prospects for observing the intermediate neutral Higgs boson (H_2) in the LEP allowed region of the parameter spaces, from the associated WH_2 production, in lepton + 4-jets (3b-tagged) + missing energy channel in the framework of CP violating MSSM with 60/fb at LHC@14 TeV. Finally, prospects for observing a light CP-odd Higgs boson, which appears naturally in models like Next-to-MSSM (NMSSM), at the upcoming colliders are discussed.   Jeudi 20 Janvier 2011 à 16h, salle 114 Antonio Enrique Cárcamo Hernández (Scuola Normale Superiore di Pisa) : Composite Vectors and Scalars in Theories of Electroweak Symmetry Breaking In the context of a strongly coupled Electroweak Symmetry Breaking, composite triplet of heavy vectors belonging to the SU(2)_L+R adjoint representation and a composite scalar singlet under SU(2)_L+R may arise from a new strong interaction invariant under the global SU(2)_L×SU(2)_R symmetry, which is spontaneously broken down to SU(2)_L+R. The first part of the talk is devoted to the study of the heavy composite vector pair production at the LHC via Vector Boson Fusion and Drell-Yan annihilation under the assumption that the interactions among these heavy vector states and with the Standard Model gauge bosons are described by a SU(2)_L × SU(2)_R /SU(2)_L+R Effective Chiral Lagrangian. The expected rates of multi-lepton events from the decay of the composite vectors are also given. The second part discusses the associated production at the LHC of a composite vector with a composite scalar by Vector Boson Fusion and Drell-Yan annihilation in the framework of a SU (2)L × SU (2)R /SU (2)L+R Effective Chiral Lagrangian with massive spin one fields and one singlet light scalar. The expected rates of same sign di-lepton and tri-lepton events from the decay of the composite vector and composite scalar final state are computed. The connection of the Effective Chiral Lagrangians with suitable gauge models is elucidated.   Jeudi 16 Décembre 2010 à 16h, salle 114 Andrea Shindler (Humboldt Universität zu Berlin) : The chiral regime of QCD I discuss the dynamics of QCD at very small up and down quark masses with two specific examples. In the first example I focus on the particular case when the correlation length is larger than the linear size of the system. I show that in this setup a combination of lattice QCD and a generalized chiral effective theory allows the determination of low energy constants (LECs) of the chiral Lagrangian. As a second example I discuss another method to determine LECs, recently introduced, which is based on the spectral density of the Dirac operator. I briefly analyze lattice results obtained from the spectral density method using as a tool a generalized chiral effective theory. ATTENTION : changement de salle   Lundi 13 Décembre 2010 à 16h, salle 110 Sasa Prelovsek (Jozef Stefan Institute/Université de Ljubljana) : Lattice QCD searches for tetraquarks and mesonic molecules I will review lattice QCD simulations of experimentally observed hadronic resonances, which are candidates for tetraquarks or mesonic molecules, for example light scalar mesons and charmonium like X(3872),Y(4140),Z(4430) states.   Jeudi 9 Décembre 2010 à 17h, Amphi 2 Giulia Pancheri (LFN Frascati) : Total cross sections at LHC Predictions for the total hadronic cross-sections at LHC from various models will be presented, highlighting differences and common features and consistency with the Froissart limit. Our model, based on the eikonal representation with QCD mini-jets to drive the rise and soft gluon resummation to tame the mini-jet rise into a behaviour in agreement with the Froissart bound, will be discussed. Within this model, the role played by soft gluon transverse momentum distributions in the infrared region will be discussed in relation to gluon saturation.   Jeudi 2 Décembre 2010 à 17h, Amphi 2 Fabien Buisseret (Université de Mons) : Glueballs : at the interface between lattice QCD and constituent models As a nonperturbative Yang-Mills theory, QCD allows the existence of purely gluonic bound states called glueballs. Since no firm experimental glueball candidate is known so far, the most fundamental data we know about these hadrons come from lattice QCD : The low-lying glueball mass spectrum obtained from lattice calculations is used both as a guide by experimentalists and as a benchmark for effective theoretical approaches of QCD. In the present talk I will focus on constituent models, i.e. models assuming that glueballs are bound states of constituent gluons, in the spirit of, say, naive quark models for mesons and baryons. We will see that lattice data can be used to constrain the existing constituent models and that, in turn, these models are able to satisfactorily reproduce the glueball mass spectrum. Emphasis will be put on the complementarity of both lattice QCD and effective approaches in order to reach a better understanding of glueball physics.   Lundi 22 Novembre 2010 à 16h, salle 114 (séminaire commun LPT/IPhT) Boris Ermolaev (IPTI St-Petersburg) : Factorization in QCD and requirements for the non-perturbative contributions to the DIS structure functions According to the factorization concept, the QCD scattering amplitudes and DIS structure functions can be represented through convolutions of the perturbative and non-perturbative (the initial parton distributions (IPD)) blobs. The both blobs are infrared -sensitive. On the other hand, the convolution of the blobs must be free of both UV and IR divergences. We show that the convolution is finite only if the non-pert blobs satisfy certain conditions. We present such conditions both for k_T and collinear factorizations. In particular we conclude that IPD for F_1 singlet can include the singular factors x^-a, however with a < 1 only. The other DIS structure functions should not include the singular factors at all.    Jeudi 18 Novembre 2010 à 16h, salle 114 François-Xavier Josse-Michaux (CFTP, IST, Lisbonne) : A Tight Connection Between Direct and Indirect Detection of Dark Matter through Higgs Portal Couplings to a Hidden Sector We present a hidden abelian extension of the Standard Model including a complex scalar as a dark matter candidate and a light scalar acting as a long range force carrier between dark matter particles. The Sommerfeld enhanced annihilation cross-section of the dark matter explains the observed cosmic ray excesses. The light scalar ï¬eld also gives rise to potentially large cross-sections of dark matter on the nucleon, therefore providing an interesting way to probe this model simultaneously at direct and indirect dark matter search experiments. We constrain the parameter space of the model by taking into account CDMS-II exclusion limit as well as PAMELA and FermiLAT data.   Mercredi 22 Septembre 2010 à 16h, salle 114 Anthony Thomas (Université d’Adelaïde) : Reassessment of the NuTeV Anomaly We reassess the claim by the NuTeV Collaboration of a three standard deviation disagreement from the Standard Model in the value of the Weinberg angle determined in neutrino-nucleus deep-inelastic scattering. The recent discovery of an iso-vector EMC effect, combined with strong theoretical constraints on charge symmetry violation lead us to the conclusion that the Standard Model still lives. We pay particular attention to the open questions which if resolved could further improve the precision of such tests.